4298 The advantage of the general formulations 1 and 2 is not only that they permit immediate solutions for the examples in ref 1 and 2, but also that they permit solution of cases of considerably greater complexity, in particular those in which the dipole vector fluctuations are not codirectional with the mean moment or with an axis of symmetry.3 Finally, the experimental data in ref 1 on e-amino caproic acid supports the general results, but does not, in my opinion, afford quantitative differentiation between the predicted values from eq l and those from eq 2.
COMMUNICATIONS TO THE EDITOR
to some extent characteristic of the corresponding alkali metal nuclei. Similar experiments carried out in DzO ices gave narrower lines, which shows that under these conditions the electron is also still interacting with the protons or deuterons in the ice matrix. Qualitatively similar results were also obtained after thermal bleaching alone. I n the bleached centers, g values for the electron were found to be: NaOH ice, 2.0056 f 0.0002; CsOH ice, 2.0048 f 0.0002; and KOHice, g = 2.0060 f 0.0004. Further annealing to about 190°K gave in all cases a single broad line which would be compatible with a BIOPHYSICS RESEARCH DIVISION WALTERSCHEIDER coagulation of the alkali atoms. The power saturation behavior of the bleached and of the coagulated centers INSTITUTE OF SCIENCE AR’D TECHNOLOGY UNIVERSITY OF MICHIGAN is different from that of the trapped electron, which has ANNARBOR,MICHIGAN48107 the shape predicted by Portis7 for the case of inhomoRECEIVED MAY4, 1970 geneous broadening, whereas the bleached centers do not show power saturation under these conditions. The hyperfine splitting of the spectra obtained after bleaching and annealing as described above could have an origin similar to that of impurity donor states in On t h e Nature of Bleached Color Centers centain matrices,s and in this case could be due to the in Irradiated Alkaline Ice interaction of the electron with the nuclear moment of the corresponding (hydrated) allrali ion nucleus. The Sir: y-Irradiation of alkaline i ~ e l -at~ 77°K leads to number of hyperfine lines corresponds roughly to the the formation of color centers 585 nm) which nuclear spin of the respective alkali nuclei (NaZ3,I = can be bleached by visible light. This is another fea3/2; Csla3,1 = 7/2) so that one may conclude that in ture which emphasizes a similarity between trapped the bleached centers the electron is to some extent electrons in ice matrices and the F-centers in irradiated localized on the cation. However, the observed hyalkali halides. More recently bleached F-centers in perfine spectra show unequal intensities and some asymalkali halides have been studied by Noble6 and Markmetry. This could be due to the superposition of a ham who, however, did not reach any definite conclusecond spectrum, particularly that associated with the sions regarding the nature of these centers. broad line which appears after further annealing, Ice matrices containing above 5 M alkali hydroxide presumably due to coagulated alkali atom centers are glassy and on y irradiation at 77°K give esr spectra which may already be formed t o a greater or lesser due to 0- ions and trapped electrons (et-). At lower extent during the earlier stages of annealing. alkali concentrations one obtains polycrystalline speciTheoretically, the total hyperfine separation between mens which show an additional resonance due to OH the extreme lines of the multiplets should be proporradicals, but annealing at 110°K leaves only the 0tional to the magnetic moment of the nucleus of the and et- ~ p e c t r a . ~ cation and the square of the (normalized) wave function The experiments reported below were carried out of the electron at the alkali nucleus.* The observed with 1 M alkaline ices (NaOH, KOH, and CsOH). total hyperfine separations in the ice matrices of 1 M Samples were prepared by the method described prealkali hydroxides were found to be: CsOH, 98.8 f viously.6 6oCo y radiation at a dose rate of 0.1 &had/ 1.0 G ; NaOH, 44.6 f 1.0 G; and KOH, 30.0 f 1.0 G. hr was used with a total dose of 1.5-2.0 Mrads. Measurements were made on a “Microspin” esr spectrome(1) D. Schulte-Frohlinde and K . Eiben, 2.Naturforach., A, 17, 445 ter operating at 9.4 kR!tHz. Samples were annealed to (1962). the required temperature and then recooled to 77°K (2) B. G. Ershov, A . K. Pikaev, P. Ya. Glaaunov, and V. I . Spitsyn, Dokl. Akad. Nauk SSSR, 149,363 (1963). for taking spectra. Photobleaching was carried out (3) M. J. Blandamer, L. Shields, and M. C. R. Symons, Nature, 199, with a 500-W tungsten lamp. 902 (1963). Esr studies on the bleached color centers in the 1 M (4) P. N. Moorthy and J. J. Weiss, Phil. Mag., 10, 659 (1964); Adw. Chem. Ser., 50, 180 (1965). alkaline ices showed that the spectra were different (5) G. A. Noble and J. J. Markham, .J. Chem. Phys., 36, 1340 from that of the trapped electron before bleaching. (1962). For these measurements the specimens were first (6) L. Kevan, I?. N. .Moorthy, and J. J. Weiss, Nature, 199, 689 annealed to 110°K to remove the OH radicals. After (1963); J. Amer. Chem. SOC.,8 6 , 771 (1964). further annealing to 170°K (when the 0- resonance (7) A. M. Portis, Phua. Rev., 91, 1071 (1953). also disappears) a hyperfine structure reveals itself (8) J. M. Luttinger and W. Kohn, ibid., 97, 883 (1955). The Journal of Physical Chemistry, Vol. 74, No. 24, 1970
COMMUNICATIONS TO THE EDITOR I n the absence of any independent knowledge of the wave function of the electron, it is not possible to test this theory. In the photobleaching and annealing of irradiated alkaline ice it has previously been suggested, firstly by Moorthy and we is^,^ that the electron combines with the corresponding hole center (0-) in the matrix ace20H-. Subsequently, cording to: O-.HzO the formation of dielectrons corresponding to the formation of F’ centers in alkali halides was also proposed. 9 , lo According to the observations reported above, there exists another possibility, i.e., that the electron is trapped in an expanded orbit of a hydrated alkali cation. Recently, Hart” reported some results from flash photolysis experiments of alkaline solutions which he could interpret on the assumption that the hydrated electron was trapped to some extent in an expanded orbit around a sodium ion. If this is confirmed, then this would represent a trapping mechanism in aqueous solution corresponding to that suggested here for ice matrices.
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Table I : Hydrogen Contents Observed in Rhodium-Palladium Alloys adter Removal from the High-Pressure Vessel Max. Hz
% Rh
Hydrogen-topalladium
Hydrogen-tometal
pressure used, a t m
5 5 5 10 10 15 20 20 20 30 30 30 40 40
0.90 f.0.02 0.86 0.95 0.99 1.02 1.07 1.15 1.26 1.22 1.34 1.44 1.46 1.52 1.61
0.86 f 0.02 0.82 0.91 0.89 0.92 0.91 0.91 1.01 0.97 0.93 1.00 1.01 0.90 0.96
2 )300 5,100 23,200 2 I 300 21,300 21,300 2,300 5,100 23,200 2,300 5,100 23)200 2,300 5,100
Alloy
added metal is believed to be, itself, a nonabsorber of hydrogen. Evidence that pure, bulk rhodium absorbs appreciable amounts of hydrogen has never been presented. l6 The hydrogen was introduced into a high-pressure vessel (25’) described elsewhere.l7 The samples were in the form of thin foil. The pressure was applied to LABORATORY O F RADIATION CHEMISTRY N. B. NAZHAT the samples in stages over a period of many hours. The THEUNIVERSITY J. J. WEISS* final pressures (Table I>were applied for a period of at NEWCASTLE UPON TYNE, NE1 7RU, ENGLAND 1 hr. The vessel was cooled (--SO0), the least RECEIVED JULY 16. 1970 samples were removed and stored in liquid nitrogen prior to their examination with X-ray diffraction and
(9) J. Zimbriclt and L. Kevan, J . Amer. Chem. SOC.,89, 2483 (1967). (IO) A. S. Khodzhaev, B. G . Ershov, and A . K . Piltaev, Izt. Akad. Nazik SSSR, (S), 1882 (1969). (11) E . J. Hart, paper presented a t the 4th International Congress of Radiation Research, Evian-les-Baine, France, July 1970. * To whom correspondence should be addressed.
Remarkable Interstitial Hydrogen Contents Observed in Rhodium-Palladium Alloys a t High Pressures
Xir: There has been considerable recent interest in the absorption of hydrogen by palladium alloys because these systems provide valuable tests for theories of hydrogen absorption. With the exception of the nickelpalladium system,l these investigations have been limited to palladium alloys in which the added metal is generally considered to absorb only insignificant amounts of hydrogen, e.g., silver-palladium, 2-5 goldpalladium,637 platinum-palladium,8~9 rhodium-palladium, lo, l 1 copper-palladium, l 2 1 l 3 tin-palladium. l4 In none of these studies have hydrogen-to-palladium atomic ratios in excess of 1 been reported; i.e., there is no evidence that the added metal absorbs hydrogen when located within the palladium matrix. In this research we wish to report for the first time hydrogen-to-palladium ratios well in excess of 1 (Ta,ble I) for an alloy system, rhodium-palladium, where the
(1) F. A. Lewis, “The Palladium Hydrogen System,” Academic Press, London and New York, N. Y. 1967. (2) G. Rosenhall, Ann. Phys. Leipzig, 24, [5] 297 (1935). (3) Z . L. Vert and I. P. Tverdovskii, Zh. 8‘6% Khim., 28,317 (1954). (4) ,E. Poeschel and H. Brodowsky, 2. Phys. Chem. (Frankfurt am Mazn), 44, 143 (1965). (5) A. Carson and F. ,4.Lewis, Trans. Faraday Soc., 63, 1447, 1453 (1967). (6) A. Maeland and T . B. Flanagan, J.Phys. Chem., 69,3575 (1965). (7) K . Allard, A. Maeland, J. W. Simons, and T . B. Flanagan, ibid., 72, 136 (1968). (8) A. I. Stetsenko and I. P. Tverdovskii, Zh. Fiz. Khim., 26, 647 (1952). (9) A. Carson, T. B. Flanagan, and F. A. Lewis, Trans. Faraday Soc., 56,371, 1311 (1960). (IO) I. P. Tverdovskii and A. I. Stetsenko, Dokl. Akad. Nauk SSSR, 84,997 (1952). (11) J. C. Barton, J. A . Green, and F. A. Lewis, Trans. Faraday SOC., 62,960 (1966). (12) R . A. Karpova and I. P. Tverdovskii, Zh. Fiz. Khim. 33, 1393 (1959). (13) D . Chisdes and T. B. Flanagan, results to be published. (14) H. Husemann, PhD Dissertation, Munster, 1968. (15) E. .Mtlller and K . Schwabe, Z . Phys. Chem. Abt. A , 154, 143 (1931). (16) A. Sieverts and E. Jurisch, Ber., 45,228 (1912). (17) B. Baranowski and W. Butjnowski, Rocs. Chem., in press.
The Journal of Physical Chemistry, Vol. 74, No. .%‘4*1.970
